1. Field of the Invention
The invention pertains to the field of endless tracks used to propel track-laying vehicles. More particularly, the invention pertains to an improved track design for a track-laying vehicle.
2. Description of Related Art
Many track-laying vehicles are driven and supported by rubber tracks. As used herein, the term “rubber” relates to any elastic and primarily non-metallic materials such as rubber, elastomers, or combinations thereof used in the manufacture of endless tracks.
There is presently an acute need for a form of vehicle appropriate for both normal highway use and off-road use over snow-covered, uneven, or muddy terrain. There is significant need for such a vehicle following natural emergencies such as snowstorms, windstorms, and floods, and such vehicles are at present particularly needed in developing countries. Unfortunately, almost all available automotive vehicles require infrastructure, including paved highways and bridges, for practical operation, and the developing countries are decades away from having the necessary infrastructure for such conventional vehicles.
Rubber endless tracks are well known and provide supporting contact between a track-laying vehicle and the terrain over which the vehicle is to be moved. The tracks are carried by a plurality of rotating elements, such as wheels and sprockets, mounted on the track-laying vehicle. The tracks are maintained in circumferential contact with these rotating elements and are driven thereby, or, in the case of trailer-like non-driven vehicles, are supported for rotation thereon.
Most tracks are formed around a basic carcass or belt element having respective interior and exterior surfaces with a predetermined width dimension co-extensive with the track's overall track width. Terrain-contacting lugs are formed integral with the exterior surface of this basic belt element. Known rubber tracks include large lugs having a variety of well-known orientations. The external lugs are formed generally perpendicular to the track axis, at an angle to the track axis, or in a chevron or modified-chevron design.
One special variety of such tracks, disclosed in U.S. Pat. No. 6,135,220 by the inventor of the present invention and incorporated herein by reference, is designed to be driven by rubber-tired wheels and has been shown appropriate for the needs of multi-use tracked vehicles that are capable of being driven at highway speeds on paved highways in addition to use over uneven off-road terrain. These special tracks include interior lugs for maintaining the track in alignment as it travels over the circumferences of the rubber-tired wheels. The lugs are located in the center of the interior surface of the track for designs appropriate for fitting between the tires of dual-wheels or in two aligned rows near the outside edges of the track for receiving a single tire therebetween.
Other known rubber tracks, when mounted on the rotating wheels of vehicles, exert resistive forces that must be overcome to move the vehicle, specifically, resistive forces in addition to those forces created by the load being carried and/or generated by the terrain. These further resistive forces relate to the additional tensions required to stretch the heavy lugs of the tracks around the wheels over which they are mounted and to the additional friction generated between the tracks and the terrain. While the latter frictional resistive forces are a valuable attribute under wet or snowy conditions, they add undesirably to energy costs when driving the vehicle over flat, hard surfaces.
U.S. Pat. No. 6,241,327, also by the inventor of the present invention and incorporated herein by reference, discloses improvements to track designs that increase the efficiency of the off-road/highway-speed tracks specifically designed for multi-use tracked vehicles. In one improvement, a relatively thin cut is made in each lug portion of the tracks. In the preferred embodiments of the invention, the cut is made perpendicular to the track's central plane and parallel to the axes of the vehicle's rotating drive/support elements, and the cut is made throughout substantially the entire thickness dimension of each lug down to the exterior surface of the carcass belt. This improvement reduces the force required to stretch the heavy lugs of the track as the track changes direction when being moved over the circumferential surfaces of the rotating elements of the vehicle's track suspension system.
In a second improvement in U.S. Pat. No. 6,241,327, the track design includes a lug modification that is particularly applicable to those endless tracks used for suspension systems in which the track is supported and driven by rubber-tired wheels. This further modification selectively reduces the thickness of each lug by tapering each lug outboard of that central portion of the basic carcass/belt that is in direct contact with the rubber-tired supporting wheels. This modification reduces drag when driving over paved surfaces, while still providing desired additional traction when traversing wet or snow-covered terrain. This taper also facilitates pivot turning.
Prior to the present inventor's track design, load-carrying off-road vehicles had either very large wheels or very cumbersome tracks, which are heavy, slow-moving, and inappropriate for use on paved roads at normal highway speeds. While smaller all-terrain wheeled vehicles are commercially available, these do not carry adequate loads for normal multi-passenger or produce transport, and their drive wheels can easily become mired in heavy mud or snow. Therefore, track-laying vehicles of the type disclosed in the above-identified patents promise great utility for the future.
Although the track designs patented in U.S. Pat. No. 6,241,327 offer superior combinations of off-road, highway speed, and load carrying capabilities, the present inventor has found that under certain conditions the endless track may experience an undesirable “roll-out”. That is, when only the outer edge of the track passes over a sharply uneven terrain, a severe twisting of the track belt can, in some instances, cause the guide lugs to tip out of the mating surfaces formed between the two supporting dual wheels, thereby dislodging the endless track laterally out of its normal alignment. Therefore, there is a need in the art for an improved endless track design with reduced roll-out.